A normal desirable range for whole blood folates was established using a new gas chromatography/mass spectrometric folate assay. Levels of whole blood folate in 79 normal individuals were assessed and homocysteine (a marker for folate deficiency was also evaluated on day 1, 5 and 8 of folate administration). A desirable range for the new red blood cell folate assay was obtained and it was observed that homocysteine variations from baseline were as wide as 29-241% of baseline levels while patients were on folate supplementation. This data indicates that homocysteine is too insensitive to assess subclinical folate deficiency because of the wide range in normal individuals and that the new whole blood folate assay can establish lower limits of normal for clinical and subclinical folate deficiency.